The lower level python serial implementation can be found in the serial.py file. You may be able to make the changes here. To make your changes take effect call the init method of the USART object like this
target.ser.cwlite_usart.init()
If you want an easier way just to change the baud rate you can use
target.baud = 3XX, YYY
these objects will be available in the python console after running the connect_cwlite_simpleserial.py script.
Hope this helps!